Distribution and source identification of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in surface soils and chicken eggs in the vicinity of Oroville, California

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/PCDF) are persistent, toxic and bioaccumulative pollutants that enter the food chain through aerial deposition of combustion and industrial emissions. There are multiple PCDD/PCDF point sources in the small northern California city of Oroville, including several former wood treatment facilities and a former waste-to-energy cogeneration plant. Surface soil samples were collected throughout the Oroville area to determine the current extent and distribution of aerially deposited PCDD/PCDF (n=38). Recently collected chicken egg samples (n=14) were also compared to understand the relationship between PCDD/PCDF in soil and PCDD/PCDF in eggs produced by chickens foraging on impacted soils. Results ranged from 0.018 to 1,000 ppt Toxic Equivalents (TEQ) for soils and 0.004 to 14.7 ppt TEQ for eggs, and averaged 63.9 and 2.58 ppt TEQ, respectively. Elevated areas of PCDD/PCDF in soil did not coincide with elevated areas of PCDD/PCDF in chicken eggs, suggesting that bioaccumulation can occur even when chickens are exposed to moderate levels of PCDD/PCDF in soil. Hierarchical cluster analysis (HCA) was used to compare soil and egg PCDD/PCDF congener toxicity patterns to waste ash, air emissions and soils collected from local PCDD/PCDF point sources. The collected soil and egg samples resembled at least one of two distinct PCDD/PCDF sources: a former wood treatment plant and a former cogeneration plant. Samples associated with both PCDD/PCDF point sources exhibited distinctly different distribution patterns, which were consistent with the varying congener compositions and emission conditions at the two facilities. PCDD/PCDF associated with the former cogeneration plant were broadly distributed over a large area while PCDD/PCDF from the former wood treatment facility were deposited closer to the facility and only along the direction of prevailing wind. PCDD/PCDF were identified in soils and correlated with known point sources 15 years after PCDD/PCDF were emitted, indicating PCDD/PCDF are persistent in soils and leave a toxic legacy long after deposited. These findings have great implications for residents who raise and consume home-produced animal products in the Oroville area and may be exposed to PCDD/PCDF through bioaccumulation.